1. Field of the Invention
The present invention relates to tray distillation columns in which the gases and vapors subdivided into separate streams meet counter-currentwise a liquid phase flowing helically from one tray to another.
It relates more particularly to a distillation column in which the trays in the form of a semicircle are disposed alternately on each side of a continuous vertical wall and therealong, said wall dividing the column into two sectors sealed to the passage of the vapors, each of which houses a series of trays, the successive trays of the same series being separated by a fixed distance D, each tray having at one of its edges a liquid reception area and at the other a cut section forming the overflow, said reception areas and said overflows being situated alternately in the succession of superimposed trays sometimes at one side and sometimes at the other side of a plate, so that the liquid follows a helical path.
2. Related Art
Such columns are known and one of them is described in the French Pat. No. 85 01874 in the name of the applicant.
Please refer to FIG. 1. So as to maintain a high hourly distillation rate, attempts are made to provide maximum liquid and vapor flow rates in the column. The value of these flow rates determines the pressure loss of the gas and vapor stream rising from one tray to another. Furthermore, this pressure loss and the liquid flow rate govern the determination of the height h of the liquid filling the overflow well feeding each tray. This height h is a parameter which is taken into account at the time of designing the distillation column, particularly for determining the spacing D between the trays, which is usually of the order of 2 h, except in the case where driving of the liquid by the gas phase imposes a higher constraint.
The pressure loss .DELTA.p of the gas and vapor stream rising from one tray to another is related both to this height h and to the spacing D of these successive trays.
In a conventional column providing a crossed stream of liquid with respect to the gas and whose design was defined by fixing the value of D with respect to the desired liquid flow rates, the spacing D between the successive trays is constant.
In fact, since the rising gases and vapors experience the same decrease of the pressure loss .DELTA.p, whereas the downgoing liquid meets the same pressure increase .DELTA.p in each gap between successive trays, there is no reason to design any dissymmetric spacing between successive trays.
It is quite different for a half plate column with helical flow of the liquid. Let it be assumed that, in such columns, the gases of a given stream rising inside a given sector of the column continue to experience an equal decrease of the pressure loss .DELTA.p from one tray to another. In such case, it is possible for liquid, (depending on whether it passes during its helical travel for example from left to right or from right to left,) to sometimes meets, when changing sector, the same pressure when passing from a half tray of a first sector to another half tray of the second sector, above which trays, called plates of the same order or isobars, the same pressure exists. On the other hand, it is possible for the liquid to sometimes meet a different pressure when passing from a half tray of the second sector to another half tray of the first sector, where a pressure exists that is increased by a pressure loss .DELTA.p, with respect to the first half tray.